Coal is usually burned either in a bed or if pulverized and atomized in the form of fine particles. When the coal contains substantial amounts of sulfur this is transformed into oxides of sulfur, mostly sulfur dioxide, during combustion. Sulfur oxides constitute serious atmospheric pollutants and in recent years quite stringent standards have been set in the United States for the concentration of sulfur oxides which can be vented to the atmosphere. This has required either low sulfur coal, about 1% or less, or the coal can be treated to remove excessive sulfur. In either case, there is a substantial penalty. It has therefore been proposed to mix finely divided lime or limestone with the coal and during burning a considerable amount of sulfur dioxide is oxidized in the combustion process which always has excess oxygen and calcium sulfate is produced. The removal of the particulate calcium sulfate can be effected by conventional means such as electrostatic precipitation. Combustion is not as complete as could be desired and unless there is a very large excess of lime the amount of sulfur oxides removed can be insufficient in the case of high sulfur coals.
It is with an improved coal fuel that the present invention deals and problems such as explosion hazards in powdered coal plants that are not kept scrupulously clean are avoided.